A young Viking befriends a creature that is his sworn enemy. With Jay Baruchel, Gerard Butler, America Ferrera. Directors: Dean DeBlois, Chris Sanders (1:38). PG: Fiery and growly battles. At area theaters.

Dragons, second only to dinosaurs and fairies in their grasp on young imaginations, are a natural selection for computer animation. The visually thrilling 3-D film of "How to Train Your Dragon," adapted from the best-selling series of kids' books, makes the most of the its format, soaring when its young hero rides on his winged reptilian pal, and full of heart and heroism even when its action is grounded.

In a long-ago world, a tribe of Vikings on the island of Berk are constantly readying themselves against regular dragon attacks. The fire-breathers, a Technicolor breed that comes in every shape and size, swoop from the skies to steal livestock, anger the Viking chief Stoick the Vast (Gerard Butler) and basically wreak havoc.

Stoick's son, a scrawny and thoughtful would-be blacksmith named Hiccup (Jay Baruchel), is physically and temperamentally unfit for fighting. Even he can't escape the boot camp every Viking teenager must endure to prepare for dragon battle, though. Hiccup's class includes Fishlegs (Christopher Mintz-Plasse), Snotlout (Jonah Hill) and the stout-hearted Astrid (America Ferrera), a young, fightin' lass who maybe likes Hiccup as much as he likes her.

After secretly rescuing a wounded dragon he names Toothless, Hiccup discovers the "monsters" aren't as mean as he was led to believe. Thanks to Toothless, Hiccup learns how to soothe dragons, talk to them and negotiate with them. Then, when Stoick uses an innocent Toothless to help him find the dragons' nest, Hiccup has to teach his friends some dragon-calming skills in order to save all their families.

The vocal performances by Baruchel, Hill and Mitnz-Plasse lend a slacky jokiness to the movie, though Ferrera, Craig Ferguson (as a grumpy tinkerer) and "SNL's" Kristen Wiig - she's one half of a dim-witted twin team - make just as much of an impression. The thrust of "Dragon," however, is the sweet connection between a boy and his beast, and the fact that Toothless is voiceless - an important decision in an animated movie - lends a classic touch to this technically up-to-the-minute movie.

And that may be what younger kids will likely appreciate about it (those older than 7 should have no problems at all, not even with a giant cave creature's three-dimensional jaws). Though the dragons are cool in their various forms and the battle scenes are epic and exciting, watching two former foes become friends is what really makes the story fly.